cpu/atmega32u4: Removed incorrect interrupt
cpu/atmega32u4: Removed incorrect interrupt

Currently the configuration claims that external interrupt INT4 is present on
pin PE7. However, the ATmega32U4 datasheet (section 10.3.4 page 81) contains
the following remark to pin PE7: "Not present on pin-out". This commit removes
the PE7 from the interrupt config.

kaspar030/RIOT,rfuentess/RIOT,josephnoir/RIOT,ant9000/RIOT,RIOT-OS/RIOT,kaspar030/RIOT,yogo1212/RIOT,OlegHahm/RIOT,OlegHahm/RIOT,x3ro/RIOT,aeneby/RIOT,yogo1212/RIOT,jasonatran/RIOT,kaspar030/RIOT,ant9000/RIOT,OTAkeys/RIOT,miri64/RIOT,yogo1212/RIOT,OlegHahm/RIOT,smlng/RIOT,authmillenon/RIOT,yogo1212/RIOT,basilfx/RIOT,aeneby/RIOT,RIOT-OS/RIOT,toonst/RIOT,kYc0o/RIOT,toonst/RIOT,cladmi/RIOT,basilfx/RIOT,kYc0o/RIOT,authmillenon/RIOT,smlng/RIOT,ant9000/RIOT,mtausig/RIOT,authmillenon/RIOT,josephnoir/RIOT,OTAkeys/RIOT,miri64/RIOT,smlng/RIOT,RIOT-OS/RIOT,cladmi/RIOT,ant9000/RIOT,authmillenon/RIOT,mtausig/RIOT,authmillenon/RIOT,toonst/RIOT,basilfx/RIOT,rfuentess/RIOT,OlegHahm/RIOT,x3ro/RIOT,toonst/RIOT,kaspar030/RIOT,kYc0o/RIOT,kaspar030/RIOT,kYc0o/RIOT,josephnoir/RIOT,smlng/RIOT,mtausig/RIOT,jasonatran/RIOT,aeneby/RIOT,rfuentess/RIOT,x3ro/RIOT,RIOT-OS/RIOT,josephnoir/RIOT,OlegHahm/RIOT,miri64/RIOT,basilfx/RIOT,OTAkeys/RIOT,x3ro/RIOT,mtausig/RIOT,cladmi/RIOT,aeneby/RIOT,RIOT-OS/RIOT,smlng/RIOT,yogo1212/RIOT,jasonatran/RIOT,OTAkeys/RIOT,yogo1212/RIOT,authmillenon/RIOT,OTAkeys/RIOT,jasonatran/RIOT,x3ro/RIOT,basilfx/RIOT,ant9000/RIOT,jasonatran/RIOT,aeneby/RIOT,cladmi/RIOT,miri64/RIOT,rfuentess/RIOT,toonst/RIOT,kYc0o/RIOT,cladmi/RIOT,mtausig/RIOT,miri64/RIOT,josephnoir/RIOT,rfuentess/RIOT